Turbine Disk Research Articles

An AK‐MCS‐based probabilistic fatigue life prediction framework for turbine disc with a mean stress correction model

AbstractThe turbine disc plays a crucial role in aerospace engine, significantly influencing both their fatigue life and overall reliability. Due to the substantial uncertainties present, devising a method for the probabilistic analysis of turbine disc fatigue life becomes crucial. This paper introduces a novel framework that combines adaptive Kriging Monte Carlo simulation (AK‐MCS) with a mean stress correction model to evaluate fatigue life distribution effectively. AK‐MCS, stands out as an algorithm that constructs a Kriging model, effectively reducing the need for an extensive finite element analysis. Furthermore, a mean stress correction model is proposed for the Masson‐Coffin equation tailored for fatigue life prediction of GH4133 disc material. This model has been empirically validated to be effective. The presented framework for probabilistic fatigue life analysis not only holds considerable engineering value but also offers innovative approaches for tackling analogous challenges in the field.

2D and 3D characterization of oxidation‐fatigue mechanisms in an advanced Ni‐based superalloy: Effects of microstructure and elevated temperature

AbstractThe effects of varying γ′ size and grain boundary carbide distribution at elevated temperatures on the fatigue behavior of turbine disk alloy RR1000 were examined through combining 2D and 3D imaging characterization. The fatigue crack growth rate at 725°C is higher than at 650°C due to enhanced oxidation damage at higher temperature, dominated by an intergranular fracture mode. This is more marked with longer dwell time (linked to diffusion time) and when carbides have formed continuously at grain boundaries. The fatigue crack path was characterized by X‐ray CT scan to present the complex 3D crack propagation morphology. It is noted that a discontinuous crack path and uncracked ligaments can be discerned ahead of the crack tip particularly in the microstructure where carbides are continuously formed at grain boundaries. This is linked to embrittled zones ahead of the crack tip formed during longer dwell times at the maximum stress during cycling at elevated temperature.

Studying the Effect of Elastoviscoplastic Modeling on Burst Speed Margins of Turbine Disc

Abstract: Aero engine turbine discs are critical components that can shatter owing to excessive mechanical loads during operation, endangering aircraft safety. Understanding burst speed margins, the buffer between maximum and actual rotational speeds, is essential for ensuring safety. ANSYS APDL software is used to examine a 2D axisymmetric non-uniform turbine disc utilizing INCONEL 718 and Ti-6Al-4V materials and numerous models. This research, which includes centrifugal, gas, and thermal loads, accurately predicts burst speed and confirms linear elastic analysis. For elastic-plastic analysis, Robinson's criterion is utilized, Perzyna for elastoviscoplastic behavior, and Bilinear isotropic hardening for elastic-plastic behavior. A sensitivity analysis of Perzyna model parameters reveals that elastoviscoplastic analysis yields higher burst margins than elasticplastic analysis for this turbine disc. The parameters are calibrated using existing models from the Literature.

Zone‐based failure risk assessment of fatigue crack growth caused by initial defects in powder turbine disc

AbstractIn this research, A zone‐based failure risk assessment (FRA) method of fatigue crack growth (FCG) caused by initial defects in the FGH96 alloy turbine disc is developed. Firstly, the initial defects distribution in the FGH96 alloy turbine disc is calculated based on the defect data. Subsequently, a probabilistic short FCG life model is established, taking into account the dispersion in grain size. Meanwhile, a probabilistic long FCG life model is established, incorporating the life dispersion factor. To calculate the Stress Intensity Factor (SIF) at any position of the disc, the general weight function method and the rectangular plate model are established. Finally, the zoning process is established, enabling a FRA that considers the FCG due to initial defects. The results indicate that the number of cycles corresponding to a 0.13% failure probability of the turbine disc is 7150, and the percentage of failures in each zone is analyzed.

Study of nano-broaching properties on nickel-based high-temperature alloys based on molecular dynamics simulation

Broaching technology, as the preferred high-volume machining process for nickel-based high-temperature alloy turbine disk tongue and groove machining, directly determines the reliability and stability of the turbine disk during its service. Although a host of scholars have carried out extensive experimental studies on the broaching process, there are few reports on the exploration of the atomic scale response in the broaching process. In this paper, the plastic deformation, defect evolution and distribution, surface formation, and stress changes during nano broaching of nickel-based single-crystal alloys are analyzed based on the molecular dynamics simulation (MD) method to reveal their broaching properties. The results show that the thermal softening effect induced by the accumulation of cutting temperature is the main reason for the violent plastic deformation within the matrix. The phase transition of the matrix structure, the depth of the subsurface damage layer, and the dislocation density increase with the increase of the cutting distance at the initial stage of the broaching process, and then slow down the upward trend at the stable broaching stage, and fluctuate in a certain range gradually. Meanwhile, the sources of atoms in chips produced by different broaching teeth in the broaching process alternates with the cutting distance. In addition, the diffusion depth of hydrostatic pressure and von Mises stress increases significantly with the increase of broaching distance. The simulation results can provide atomic-scale details for the broaching process of single-crystal Ni Fe Cr alloys and help to optimize the nano-broaching process of nickel-based high-temperature alloys.

Investigation of the precipitation behavior and its role on creep deformation and failure mechanisms at high temperatures for a turbine disk alloy

The creep deformation behavior of a turbine disk alloy at high temperatures was studied, and the role of the multi-scale precipitates on the creep deformation and failure mechanisms was revealed. The turbine disk alloy shows a typical microstructure with the micron-scale MC carbides, submicron delta phase, together with nanoscale γ″ and γ' precipitates distributed in the matrix after hot working and aging treatment. The MC carbides are mostly formed from the solidification process due to enrichment of Nb in the inter-dendritic areas. The creep life decreases from 763.5 h to 5.7 h when the creep temperature increases from 953 K to 1023 K at 500 MPa. The fracture surfaces exhibit a transgranular fracture pattern accompanied with the formation of substantial microvoids. Slipping occurs in both unidirectional and bidirectional modes during deformation. The microvoids along the grain boundaries are generated through decohesion of δ precipitates from the matrix or the interaction between slip traces and grain boundaries. When the intragranular MC carbides interact with the slip traces, microcracks can be formed by particle fracturing. The dense distribution of particles along the grain boundaries will result in a significantly higher critical stress required for microvoid nucleation, whereas the non-coherent particles inside the grains, particularly the large size MC carbides, can decrease the critical shear stress for microcrack formation to as low as 88.9 MPa, thereby contributing to alloy rupture. For the coherent precipitates, a comprehensive strengthening effect of 389.12 MPa is achievable by the synergistic precipitation of γ″ and γ', which primarily serve to enhance and coordinate intragranular deformation during creep.

Low cycle fatigue behavior and life prediction of a directionally solidified alloy

Low cycle fatigue behavior and life prediction of a directionally solidified alloy

Effects of Pore Distribution on Mechanical Properties of Selective Laser Melted Inconel-718

In recent years, Selective Laser Melting (SLM) technology has made significant advancements, offering high precision and near-net shaping capabilities that are widely applicable in aerospace, mechanical, and electrical industries. Inconel-718, known for its exceptional high-temperature corrosion resistance, fatigue endurance, and wear resistance, has found extensive use in aerospace applications such as gas turbine disks, rocket engines, and spacecraft components. However, the presence of porous defects in SLM-manufactured metal parts is inevitable, and these pores significantly affect the mechanical properties of the materials. While contemporary studies have focused on the influence of individual or a limited number of pores, the impact of pore distribution has been largely overlooked. This oversight leads to reduced prediction accuracy and hampers the practical implementation of SLM technology. Therefore, this paper specifically investigates the impact of pore distribution on the performance of SLM-manufactured metal materials, using Inconel-718 as an example. The study establishes simulation experiment models to explore diverse pore distribution patterns, including spatial position distribution models and spatial quantity distribution models. The Finite Element Method (FEM) model utilizes the Johnson-Cook constitutive model, and the pores are equivalently modelled as two-dimensional plane ellipses. Uniaxial tension simulations are performed to analyze the mechanical behavior of the materials. The results demonstrate that the mechanical properties of SLM-fabricated Inconel-718 are significantly influenced by the spatial position distribution, spatial quantity distribution, and spatial orientation distribution of the pores. Under different spatial position distributions, materials with more pores parallel to the stretching direction exhibit poorer mechanical performance due to earlier and more significant stress concentration. Under different spatial quantity distributions, materials with a higher pore density and smaller pore spacing show worse mechanical performance due to earlier and more severe stress concentration. Under different spatial orientation distributions, materials with a larger angle between the pore’s major axis and the stretching direction exhibit worse mechanical performance due to enhanced stress and earlier and more severe stress concentration. Overall, this study highlights the importance of considering pore distribution in SLM-manufactured metal materials, providing insights into the impact of spatial position, quantity, and orientation distributions on the mechanical properties of Inconel-718.

Effect of Impellers on the Cooling Performance of a Radial Pre-Swirl System in Gas Turbine Engines

Impellers are utilized to increase pressure to ensure that a radial pre-swirl system can provide sufficient cooling airflow to the turbine blades. In the open literature, the pressurization mechanism of the impellers was investigated. However, the effect of impellers on the cooling performance of the radial pre-swirl system was not clear. To solve the aforementioned problem, tests were carried out to assess the temperature drop in a radial pre-swirl system with various impeller configurations (impeller lengths l/b ranging from 0 to 0.333). Furthermore, numerical simulations were used to investigate the flow and heat transfer characteristics of the radial pre-swirl system at high rotating Reynolds numbers. Theoretical and experimental investigations revealed that the pre-swirl jet and output power generate a significant temperature drop, but the impellers have no obvious effect on the system temperature drop. By increasing the swirl ratio, the impellers reduce the field synergy angle and thus improve convective heat transfer on the turbine disk. In addition, increasing the impeller length can reduce the volume-averaged field synergy angle and improve heat transfer, but the improvement effectiveness decreases as the impeller length increases. Thus, the study concluded that impellers could improve the cooling performance of the radial pre-swirl system by enhancing disk cooling.

Chatter Stability Prediction for Deep-Cavity Turning of a Bent-Blade Cutter.

The bent-blade cutter is widely used in machining typical deep-cavity parts such as turbine discs and disc shafts, but few scholars have studied the dynamics of the turning process. The existing mechanism of regenerative chatter in the metal-cutting process does not consider the influence of bending and torsional vibration, the change of tool profile and the complex machining geometry, so it cannot be directly used to reveal the underlying cause of the chatter phenomena in the deep inner cavity part turning process. This paper attempts to investigate the dynamic problem of the bent-blade cutter turning process. The dynamic model of a bent-blade cutter is proposed by considering the regenerative chatter effect. Based on the extended Timoshenko beam element (E-TBM) theory and finite element method (FEM), the coupling between the bending vibrations and the torsional vibrations, as well as the dynamic cutting forces, are modeled along the turning path. The vibration characteristics of the bending-torsion combination of cutter board and cutter bar, together with the dynamical governing equation, were analyzed theoretically. The chatter stability of a bent-blade cutter with a bending and torsion combination effect is predicted in the turning process. A series of turning experiments are carried out to verify the accuracy and efficiency of the presented model. Furthermore, the influence of cutting parameters on the cutting process is analyzed, and the results can be used to optimize the cutting parameters for suppressing machining vibration and improving machining process stability.

High performance machining simulation of curved edge broach with surface material constitutive model and tool-chip friction

Curved edge broaches can significantly improve the machining efficiency and accuracy of key components of aviation engine turbine discs. However, existing constitutive models and friction models fail to describe these parameters accurately during the broaching process. Therefore, this paper proposes modifications to the J-C constitutive model based on the MSG model and the friction model based on the SCG model, which are applied to an Inconel 718 simplified tenon broaching finite element model. The single-stage modification involves modifying the constitutive model first, followed by modifying the friction model from the modified constitutive model to achieve cascade correction. To verify the accuracy of the model, a simplified tenon broaching experiment is conducted, and the predicted broaching force, broaching temperature, and chip morphology are compared with experimental results. In conclusion, the modified constitutive model proposed in this paper has an accuracy of approximately 90 %, which represents a 33.3 % error reduction compared to that of the conventional constitutive model. Furthermore, the accuracy of the cascade modified model proposed in this paper can be nearly 95 %, resulting in an error reduction of about 50 % based on the modified constitutive model. The newly proposed cascade correction model can help optimize tool and process parameters in tenon broaching to achieve the desired broaching force, broaching temperature, and chip morphology using simulation-based optimization.

Estimation of stress intensity factor for surface cracks in the firtree groove structure of turbine disk using pool-based active learning with Gaussian Process Regression

Estimation of stress intensity factor for surface cracks in the firtree groove structure of turbine disk using pool-based active learning with Gaussian Process Regression

A parametric study of a bolted joint rotor-bearing system with an unbalanced offset disk

The turbine disk is the core component of an aero-engine whose position and unbalanced force seriously affect the vibration stability of the rotor system. Ignoring the influence of the offset disk may result in discrepancies between real-world scenarios and numerical simulation results. The present work aims to explore the nonlinear dynamic characteristics of rotor systems under the coupling of bolted joint and offset disk effect, as well as the influence of offset disk position and its unbalanced force on the system dynamic behavior and bending stiffness of bolted joint also investigated. The governing equations of a bolted joint rotor-bearing system with an offset disk were established based on the finite element method and derived as a dimensionless expression in the first. Then, the Newmark method was employed for the numerical solution of the motion equations, and then a bifurcation analysis of the rotor system and the evolution of bending stiffness for the bolted joint was studied. Next, by comparing the frequency-amplitude diagrams, bifurcation diagrams, time history, shaft obits, and bending stiffness diagrams of the bolted joint, the effect of the offset disk position and its unbalanced force on the nonlinear system dynamic was revealed. Finally, an experimental study was carried out to verify the numerical result using the bolted joint rotor test rig with an offset disk. The analysis result of the present work can provide theoretical guidance for structure design and stability analysis on the aero-engine.

Combined high and low cycle fatigue analysis of FGH96 alloy under high temperature conditions

The FGH96 alloy as a common material for preparing turbine discs, can withstand high- and low-cycle combined loading during service, which significantly affects its fatigue performance. In this work, the combined high and low cycle fatigue (CCF) behavior of the FGH96 alloy was explored at various low cycle stress amplitudes (600, 630, 650, 680, and 700 MPa) using a self-improved experimental platform at a high temperature of 650 °C. The results indicate that increasing the amplitude of the low-cycle stress decreases the service endurance of the FGH96 alloy at CCF condition. Under the same low cycle stress amplitude, its CCF life of alloy is lower than the pure low cycle fatigue life. A fatigue service life prediction model, grounded in the theory of crystal plasticity, has been developed to assess the combined fatigue service life across different low-cycle stress amplitudes. A comparison between the predicted and actual lifespan showed that the predicted lifetime fell within a range three times the scattering band.

Numerical and Experimental Investigation of the Thermomechanical Loads on the Machined Surface when Cutting Inconel DA718

In metal cutting processes, the thermomechanical loads lead to modifications of the residual stress state of the workpiece rim zone. Especially for aerospace components, such as turbine disks made of nickel-based alloys, this modification affects the functionality and dimensional accuracy of the machined part. Therefore, the thermomechanical loads occurring in the orthogonal cutting of Inconel DA718 are investigated in this paper and chip formation simulations are performed and evaluated with the experimental results. The outcome of this work forms the basis for a research project, where it is intended to develop a multiscale prediction model for residual stresses.

Tensile and creep properties of novel powder metallurgy Ni-based superalloy

The development of novel powder superalloys for aero-engine turbine disks holds significant implications. In this paper, the microstructure and mechanical properties of a novel powder nickel-based superalloy are evaluated, followed by a brief discussion of the relationship between tensile and creep properties. The results revealed that the new alloy exhibits good microstructural stability after long-term aging and excellent tensile strength at different temperatures. In particular, the creep properties are significantly superior compared to other alloys. In addition, it is verified that the Monkman-Grant relationship modified by tensile parameters has better validity.

Non-destructive X-ray diffraction surface integrity inspection of an aeroengine component

Industry standard assessment of machined surface integrity typically requires a form of destructive testing to capture microstructural features such as white layers or distorted layers. The X-ray diffraction surface integrity inspection method (XRD-SIIM) offers a non-destructive alternative for the detection and sizing of fatigue-limiting microstructural features, without the sacrifice or alteration of a component which is required for cross-sectional microscopy. In this study XRD-SIIM was used to measure the surface integrity across a nickel-based superalloy gas turbine disc segment. XRD-SIIM microstructural feature detection and sizing models were trained and validated from a set of surfaces generated in a turning trial with a newly developed calibration procedure allowing these models to be adjusted for different instrument setups to facilitate measurement of the turbine disc segment. The non-destructive test was then able to show comparable inspection results to industry standard microscopy of microstructural features when inspecting the representative component, with over 90% of the outside surface of the component accessible by the diffractometer, and the internal surfaces accessible with appropriate hardware. Surface curvature only became a limiting factor for inspection of geometrical features with a small radius of curvature such as seal fins and the corner radii on fir tree sections.

Investigation of the Formation of Structure and Properties in a Billet Made of Heat-Resistant Nickel Alloy EP741NP, Obtained by Hot Isostatic Pressing Technology

It is known that the technology of hot isostatic pressing (HIP) can reduce the residual porosity and increase the level of physical and mechanical characteristics of products obtained by powder metallurgy methods. In modern aircraft and rocket engineering, heat-resistant heterophase nickel alloys are used, which are obtained with the use of granular metallurgy. This material is indispensable in the creation of disks of gas turbine engines (GTE), which are part of the turbine rotor and serve to install the blades. Obtaining a nonporous product made of EP741NP alloy using the HIP technology will increase the service life of the turbine disks, which is an urgent task at the present time. The aim of the work is to study the structure and physical and mechanical properties of a billet made of heat-resistant nickel alloy EP741NP obtained by the HIP method at a temperature of 1150 °C. The starting material for the preparation of the workpiece is a metal powder EP741NP, obtained by gas atomization and having a fractional composition of 20...50 microns. It is shown that the HIP process at a temperature of 1150 °C makes it possible to obtain an optimal combination of physical and mechanical properties. Based on the obtained images of powder particles and the microstructure of the work piece, the shape of the particles of the powder under study, the main category of powder granularity was determined and digital porosity analysis of the workpiece under study was performed in the Thixomet Pro software package. The changes in density and hardness along the section of the work piece were also evaluated. It has been established that at a temperature of HIP 1150 °, the average porosity is insignificant and is 0.1 %, however, as we move away from the edge of the workpiece to its center, there is an increase in the content of pores, the size of which lies in the range of 1...20 microns. It is shown that during the technological process of HIP, an arched effect is observed, the consequence of which are overestimated characteristics of microhardness and density at the edge of the work piece.

Numerical Study on the Flow and Heat Transfer Characteristics in Mortise and Tenon Gap under Rotating Conditions

Mortise and tenon are very important parts of gas turbine dealing operation safety. Additionally, the temperature distribution of the turbine blade and disk is affected by the heat transfer characteristics in its gap. Then, the S-shaped mortise and tenon gap were numerically studied under rotating conditions, and the flow and heat transfer characteristics were analyzed. First, the heat transfer coefficient (HTC) of the mortise and tenon surfaces was measured with thermochromic liquid crystal. Then, the numerical method was verified using the test results, and the grid independence analysis was conducted. Finally, the flow and heat transfer characteristics of the gap under static and rotating conditions were numerically studied, five different Reynolds numbers (Re = 15,000, 20,000, 25,000, 30,000, 35,000) and five gap widths (d = 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm) were conducted and analyzed in detail. The results show that, under the rotating condition, the pressure distribution in the gap is different from that of the static condition; the pressure increases along the radial direction due to the action of centrifugal force and reaches its maximum value at the corner of the “S” shaped structure. With the increase in Re, the heat transfer intensity of the gap increases gradually. Additionally, the heat transfer intensity of the gap increases with an increase in its width.

Enhancing elevated-temperature fretting wear performance of GH4169 by tuning wear mechanism through laser shock peening

Turbine disks and blades made of GH4169 for turbine engines are highly prone to fretting wear damage. In this work, we used laser shock peening (LSP) to improve the elevated-temperature fretting wear performance of GH4169, and the corresponding underlying mechanisms are also systematically investigated. Fretting wear experiments conducted on specimens following LSP treatment reveal that the wear resistance of GH4169 was significantly improved, namely a 12.7% reduction in average friction coefficient and a 67.0% decrease in wear rate. Multiscale electron microscopy characterizations reveal that the gradient microstructures induced by LSP serve as the main contributor, which promotes the transition of mechanisms from adhesive wear to abrasive wear, then leading to an exceptional fretting wear performance.